"It is with mixed feelings that I announce my retirement from Ulster Rugby as of the end of this season," Best told Ulster's website.

"This feels like the right time for me to go out on my terms, a luxury for which I feel very privileged.

"I am very excited for the end of the season with Ulster Rugby and for the upcoming World Cup with Ireland, both of which I hope to finish with a massive high, playing at the top of my game."

Rory Best, centre, won the Six Nations four times (Gareth Fuller/PA)

Ireland begin their World Cup campaign on September 22 against Scotland in Yokohama, with the final scheduled for November 2.

Best has led his country to as high as second in the world rankings during an international career which began in 2005, and captained the team to their first win against world champions New Zealand in 2016.

He toured with the British and Irish Lions in 2013 and 2017 – although he was not selected for a Test match – and was awarded an OBE for services to rugby in the 2017 Birthday Honours.

Rory Best was awarded an OBE in 2017 (Dominic Lipinski/PA)

Speaking about his time with Ulster, he said: "In my 15 years at this brilliant club, I have been lucky to have met, played alongside, been coached by and supported by many great people, and I would like to thank every individual for the time they have invested in me since 2004.

"I grew up supporting Ulster Rugby, have been fortunate to play and captain Ulster Rugby, and now look forward to supporting Ulster Rugby in the future with my family."

Best began his rugby development at Banbridge RFC, a team he is still involved with, while he also played at Portadown College and Belfast Harlequins RFC en route to the professional game.